Check if your username is included in the user group 'cdrom' or 'cdrw', if not yet you should include it now. also your username should be a member of the 'haldaemon' 'messagebus' and 'power' groups.
Also, since Ubuntu implements hald and dbus, under /etc/fstab put a comment '#' before the cdrw/cdrom line, to look like this:
#/dev/cdrom /mnt/cdrom iso9660 noauto,user,ro 0 0
dbus respects your fstab options and if this line is not commented out chances are it imposes the rules strictly.
It solved my problem. I hope it will solve yours this time.
hih hope it helps